Avaya BCM 2.0 IP Telephony Manual de usuario descargar pdf (Pagina 35)

Engineering guidelines 35

P0911590 Issue 02 Enterprise Edge 2.0 IP Telephony Configuration Guide

Traffic mix

This section describes what QoS mechanisms work with the IP telephony, and with

what new intranet-wide results if done.

Before putting into operation QoS mechanisms in the network, determine the traffic

mix of the network. QoS mechanisms depend on the process and ability to

determine traffic (by class) so as to provide different services.

With an intranet designed only to deliver IP telephony traffic, where all traffic flows

are equal priority, there is no need to consider QoS mechanisms. This network can

have one class of traffic.

In most corporate environments, the intranet is supporting data and other services.

When planning to provide voice services over the intranet the installer determine

the following:

• Are there existing QoS mechanisms? What kind? IP telephony traffic must take

advantage of established mechanisms if possible.

• What is the traffic mix? If the IP telephony traffic is small compared to data

traffic on the intranet, then IP QoS mechanisms can do. If IP telephony traffic

is a large amount, data services can be hit if those mechanisms are biased toward

IP telephony traffic.

TCP traffic behavior

Most of corporate intranet traffic is TCP-based. Different from UDP, that has no

flow control, TCP uses a sliding window flow control mechanism. Under this

design TCP increases its window size, increasing throughput, until congestion

occurs. Congestion results in packet losses, and when that occurs the throughput

decreases, and the whole cycle repeats.

When multiple TCP sessions flow over few congestion links in the intranet, the

flow control algorithm can cause TCP sessions in the network to decrease at the

same time, causing a periodic and synchronized surge and ebb in traffic flows.

WAN links can appear to be overloaded at one time, and then followed by a period

of under-utilization. There are two results:

• bad performance of WAN links

• IP telephony traffic streams are unfairly affected

Enterprise Edge Router QoS Support

In Enterprise Edge, the VoIP gateway and the router are in the same box. The

Enterprise Edge router performs QoS and priority queuing to support VoIP traffic.

The router supports VoIP in the following two ways:

• In a DiffServ network, Enterprise Edge acts as a DiffServ edge device and

performs packet classification, prioritization, and marking. The router performs

admission control for H.323 flows based on the WAN link bandwidth and

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Avaya BCM 2.0 IP Telephony Manual de usuario Pagina 35